1-arterenol and its acid-addition salts and preparation thereof



United States Patent l-ARTERENOL AND ITS ACID-ADDITION SALTS AND PREPARATION THEREOF Benjamin F. Tullar, East Greenbush, N. Y., assignor to Sterling Drug Inc., Wilmington, Del., a corporation of Delaware No Drawing. Application October 24, 1947, Serial No. 782,012

Claims. (Cl. 260570.6)

This invention relates to optically active forms of arterenol and to their preparation.

dl Arterenol, alpha aminomethyl 3,4 dihydroxybenzyl alcohol, is a potent synthetic sympathomimetic amine which is even more active physiologically than is l-epinephrine. Compared to l-epinephrine as a standard, dl-arterenol is about twice as effective a cardiac stimulant as it is a pressor agent (Crismon and Tainter, J. Pharmacol. and Exper. Therap., 62, 189-227 (1938). Its synthesis was carried out by Stolz and Flaecher over forty years ago, shortly after the first synthesis of dl epinephrine, but all attempts to resolve it have been unsuccessful. This failure is especially surprising in view of the fact that dl-epinephrine was resolved by Flaecher in 1908. The close relationship between the two compounds is readily apparent from a comparison of the structural formulas:

H-OQc JH-Qm-Nm The pharmacological testing, and hence the pharmaceutical utilization, of arterenol has been greatly hampered by this unavailability of the optically active forms; in this respect cf. Greer et al., J. 'Pharmacol. and Exper.

2,774,789 Patented Dec. 1 s, 195

2 a ethyl alcohols than is the corresponding anhydrous d -arterenol salt. d-Arterenol does not form a salt hydrate with d-tartaric acid, l-malic acid, or N-benzoyl-l-threonine under these conditions. In complementary fashion, l-arterenol yields anhydrous salts with l-tartaric acid,

d-malic acid, and N-benzoyl-d-threonine, while with these Therap., 62, 189-227 (1938) and Crismon and Tainter (loc. cit.).

The unsuccessful results obtained by previous investigators in attempts to resolve dl-arterenol can possibly be attributed to the susceptibility of the alcoholichydroxyl group to etherification by alcoholic solvents'in the presence of acid, or to other and obscure causes. Regardless of the actual causal factors, the chief difliculty in-' volved is gum formation in the preparation of the diastereoisomeric salts.

I have now succeeded in resolving dl-arterenol into its optically active dand l-forms, thus for the first time making these isomers available for therapeutic use. Broadly, the process which I employ comprisestreating dl-arterenol with an optically active tartaric acid, malic acid, or N-benzoyl-threonine to produce a mixture of diastereoisomeric salts, separating these salts by fractional crystallization, and releasing each ofthe desired isomers, i. e. d-arterenol and l-arterenol, from the separated amine salts. An vimp ortantfeature of the invention is in the differing nature of the two diastereoisomeric salts with a given form of an optically active acid. In the presence of .sutficient water, the saltsof l-arterenol with d-tartaric acid, l-malic acid, and N- benzoyl-l-threonine will each form a hydrate which is less soluble in waterand more soluble in methyl and same acids d-arterenol forms hydrated salts. The formation of the hydrate byonly one of the two diastereoisomeric forms affords afavorable solubility difierential between the l-arterenol saltand the d-arterenol salt, thus permitting their separation by. fractional crystallization. d-Arterenol and l-arterenol are then obtained by treating the separated-salts witha base, e. g. ammonia.

Salts of l-arterenol with d-tartaric acid, l-malic acid, and N-benzoyl-l-threonine and of d-arterenol with l-tartaric acid, d-malic acid, and N-benzoyl-d-threonine readily form the requisite hydrate in the presence of water alone, or in the presence of organic solvents containing asmuch' as about 5% water, e. g. ethanolor methanolwater mixtures. Of these optically active acids, I prefer to use d-tartaric acid since this acid is cheaper than the others and it produces salts which are readily crystallized. From a concentrated aqueous solution .of dl-arterenol with an equimolar amount of dtartaric acid, crude l-arterenol acid d-tartrate monohydrate crystallizes in about of the theoretical quantity. When 94% methanol is used as the solvent, crude d-arterenol acid d-tartrate is obtained in about 80% yield. Thus, by alternate use of these two solvents, I can effect a nearly quantitative separation of the two isomers.

If it is desired to obtain one form of optically active arterenol at the expense of the other, it is desirable to racemize the less desired form. In this way the resultant dl-form can then be employed in the resolution process to obtain a further yield of the preferred isomer. The racemization process is readily carried out by heating an aqueous solution of the optically active form of arterenol with a strong mineral acid, such as hydrochloric acid.

By direct interaction of the acid and base, there are obtained therapeutically-useful salts of l-arterenol and d-arterenol with non-toxic inorganic and organic acids,

such as hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, tartaric acid, citric acid,-succinic acid,=and the like. a a

My invention is illustrated by the'following example without, however, being limited thereto.

Example are retained for part B. The solid isthen driedin air;

There is thus obtained 135 g. of l-arterenol acid d-tartrate monohydrate, M. I. 88-95 C. This product'is dissolved in 100 ml. of de-ionized water at 50 C., and charcoal'is added to the solution, which is then filtered. The residue on the; filter is washedwith 25ml. of hot water and the combined filtrates are cooled to 0"v C.

After several hours, the solid which preoipitatesis col lected on a filter, and isiwashed with 10 ml..of ice water? and then with 95% ethanol. .The' combined filtrates and washings'are retained for part B. The washedsolid' is dried, thus yielding 88 g. of nearly pure product, M. P.

. for l-arterenol.

from an equal weight of water. There is thus obtained 60-85 g. of pure l-arterenol acid d-tartrate monohydrate, M. P. 102-1045 C., [a] -10.7 (1.6% sol-n; in water); To remove the water of hydration, if desired, one part of the hydrate is dissolved in. 10 parts of methanol, preferably at 35 C., and the solution is allowed to stand at room temperature for several hours. The solid which crystallizes during this time is then collected on a filter, is washed with methanol and. ether, and is dried at reduced pressure. There is thus obtained l-arterenol acidd-tartrate, M. P. approximately 160 C. l-Artere'nol is'iprepared by dissolving 1 part of an l-arterenol salt, ,e.--g. the acid d-tartrate, in 10 parts of water, and making the solution alkaline by adding 0.5Ipart of concentrated ammonium hydroxide, preferably at 10-15 C. On standing, l arterenol separates from the solution. This solid is :collected on a filter, is washed with water, methanol, and ether, and is dried at reduced pressure. There is thus obtained 0.5 part of l-arterenol, M, P. 2165-218" (3., [a] ---37.3 soln. in dilute hydrochloric acid). .This base reacts with acids inconventional manner to yield salts: e. g. l-arterenol sulfamate, M. P. 105-107 C.; l-arterenol sulfate, M. P.

90-94 C.; l-arterenol hydrochloride, M. P. 1465-1475 C. and lu] -39 (6% sol-n. in water); and l-arterenol d-malate, M. P. 160162 C.

B. Preparation of d-arteren0l.The two portions of filtrates and washings retained from the crystallizations in part A are combined and concentrated to dryness at reduced pressure. The residue thus obtained is dissolved in 200 rnLof methanol at 50-60 C. To the clear solution is added 1500 ml. of methanol. This solution is allowed to stand at 25 C. for several hours with occasional scratching and stirring. A mass of crystals precipitates. This solid is collected on a filter, and is washed well with methanol. The combined filtrate and washings are retained for part C. The solid is dried in air. There is thus obtained IOU-g. of d-arterenol acid d-tartrate, M. P. 161-165 C. If desired, this product can be purified by recrystallization from 94% methanol. The; pure compound melts at 1641-165" C., and has [a] .-39.9 (1.6% soln. in water). d-Arterenol, M. P. 216-217" C., [a] .37.4. (1. 6% soln. in water), is obtained by adding ammoniumhydroxide to an aqueous solution of a d-arterenol salt, using a procedure analogous to that employed in partA Salts of this base are obtained in the usual manner by interaction with acids; for example: darterenol hydrochloride, M. P. l46-l,47, C.; d-arteren01 N-benzoyl-l-threonine, Mil. 110-112 C.; and d-ar- 'terenol l-malate, 160-l62 C.

C. Recovery of isomers from mother liquors-The all) filtrate and washings retained in part B-are evaporated i to dryness at reduced pressure. The residue, which is arr-approximately 1-1 mixture of l-arterenol acid d-tartratemonohydrate and d-arterenol acid d-tartrate, is dissolved in ml. of. water and the solution is cooled to 0.C. for several hours. A second crop of nearly pure l-arterenol acid" d-tartrate monohydrate weighing 30 g. isthus obtained." From the mother liquor a second crop of d-arterenol acid 'd-tartrate, Weighing 25 g. and melting at -165 Cl, is obtained by'rcpetition of the procedure described inpart B.

D.Racemiztztion of the d -a-rterenol.-12O g. of d-arterenol is dissolved in l 'literof deionized water and 100 nil. 0fconcentratedhydrochloric acid (previously boiled for about "thirty minutes to expel dissolved air). The solution is allowed to standat 80-90 C. for two hours, excluding .airjby means of a stream of nitrogen. The solutionis cooled to 10 C. and is then made alkaline by adding 80ml. of concentrated ammonium hydroxide. The alkaline solution is allowed to stand at 10 C. for one "hour, during which time dl-arterenol crystallizes. The solidiis collected on a filter, .is washed with two 100 ml. portions, of water and then with methanol and ether, and is then dried at reduced pressure. There is thus obtained 100 g. of dl-arterenol, M. P. 189-191 C.

It will be understood that when, in the above example, there is used as the solvent 9.4% methanol instead of water, d-arterenol d-tartrate separates from the solution of the dl-mixture, and the l-arterenol d-tartrate remains in solution,'from which solutionit is isolated by removing the solvent and fractionally crystallizing the residue.

I claim:

1. A substance selected from tthe group consisting of l-arterenol and its acid-addition salts, said substance being in crystalline'and' substantially pure form and being substantially free from its'optical antipode.

2. l-Arterenol in crystalline and substantially pure form and substantially free from its optical antipode.

3. An acid addition salt of l-arterenol, said salt being in crystalline and substantially pure form and being substantially free from its'optical antipode.

4. l-Arterenol hydrochloride in crystalline and substantially pure form and substantially free from d-arterenol hydrochloride.

5. l-Arterenol acid d-tartrate in crystalline and substantially pure form and-substantially free from d-arterenol acid -d-tartrate.

6. The process for obtaining l-arterenol which comprises: treating d-l-arterenol with an optically active acid selected from the group consisting of tartaric acid, maleic acid, and Nbenzoyl-threonine in the presence of an organic solvent containing at least 5% of water; separating the diastereoisomeric salts thus formed by fractional crystallization; and regenerating l-artcrenol from the separated salt of l-arterenol.

7. The process for obtaining l-arterenol which comprises: racemizing d-arterenol by heating it with mineral acid; treating the dl-arterenol thus obtained with an optically active acid selected from the group consisting of tartaric acid, malic acid, and N-benzoyl-threonine in the presence of a solvent containing at least 5% of water;

separating the diastereoisorneric salts thus formed by fractional crystallization; and regenerating each of the two isomers, d-arterenol and l-arterenol, from the separated amine salts.

8. The process for resolving dl-arterenol which comprises: treating dl-arterenol with an optically'active acid selected from the group consisting of tartaric acid, malic acid, and N-benzoylthreonine in the presence of a solvent containing at least 5% of water; separating the diasteoisomeric salts thus formed by fractional crystallization; and regenerating each of the two isomers ,'cl-artereno] and l-arterenol, from the separated amine salts.

' 9. The process for obtaining l-arterenol which comprisestracemizing d-arterenol byheating it with mineral acid; treating the dl-arterenol thusobtained with d-tartaric acid in the presence ,of a solvent containing at least 5% of water; separating the disastereoisomeric salts thus formed by fractional crystallization; and regenerating each of the two isomers, d-arterenol andl-arterenol, from the separated'amine salts.

. 10. The process for resolving dl-arterenol which comprises: treating dl-arterenol with d-tartaric acid in the presenceof a solvent containing at least 5% of water;

f =(0therreferences'on followingpage) UNITED STATES PATENTS Stolz et a1 Nov. 7, 1933 Kharasch July 7, 1936 FOREIGN PATENTS Great Britain 1909 Austria Aug. 15, 1914 Great Britain Aug. 10, 1933 Great Britain Aug. 17, 1933 Germany May 16, 1935 OTHER REFERENCES Karrer: Org. Chem., Nordemann Pub. Co., Inc., New York, N. Y., 1938, p. 91.

6 Gilman: Org. Chem. (John Wiley and Sons, N. Y., 1938), pp. 190, 192.

Barger et aL: Chem. Abst., vol. 5, 109 (1911). Greer et al.: J. Pharm. and Exp. Therap., 62, 189-227 5 (1937).

Drill: Pharmacology in Medicine (McGraw-Hill Book Co., Inc.), 1954, p. 26/2.

Goodman et al.: The Pharmacological Basis of Therapeutics (The MacM illan 00.), 1955, p. 500. 10 

1. A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF 1-ARTERENOL AND ITS ACID-ADDITION SALTS, SAID SUBSTANCE BEING IN CRYSTALLINE AND SUBSTANTIALLY PURE FORM AND BEING SUBSTANTIALLY FREE FROM ITS OPTICAL ANTIPODE. 